Method and apparatus for measuring the purity ratio of intermediate products in sugar manufacture

ABSTRACT

The proportion of sucrose in the whole of the dissolved substances of intermediate products in sugar manufacture is measured by: measuring the refractive index n of a sample of an intermediate product, measuring the polarimetric rotation Alpha of the same sample and then combining these measurements in the relationship Alpha /n- no to produce a &#39;&#39;&#39;&#39;purity quotient&#39;&#39;&#39;&#39; (no being the refractive index of pure water.) The numerical value of this quotient varies with the temperature of the sample. Therefore the temperature of the sample is maintained constant within a certain range and an additional temperature correction is effected. In a preferred form of apparatus for performing the measuring method, the result of the calculation of the quotient is reproduced in both analog and digital form respectively for controlling automatic process control computers and for actuating a device for indicating the measurements in visible form.

United States Patent METHOD AND APPARATUS FOR MEASURING THE PURITY RATIOOF INTERMEDIATE PRODUCTS lN SUGAR MANUFACTURE 17 Claims, 2 Drawing Figs.

US. Cl ..235/151.35, 356/73, 23/253, 23/230 Int. Cl ..G01n 1 GOln 21/40Field of Search ..235/15l.35,

[56] References Cited UNITED STATES PATENTS 3,468,607 9/1969 Sloane etal. 356/73 FOREIGN PATENTS 1,095,210 12/1967 Great Britain 356/116Primary Examiner-Eugene G. Botz Attorney-Sandoe, Neill, Schottler &Wiltstrom ABSTRACT: The proportion of sucrose in the whole of thedissolved substances of intermediate products in sugar manufacture ismeasured by: measuring the refractive index n of a sample of anintermediate product, measuring the polarimetric rotation a of the samesample and then combining these measurements in the relationship a/n-nto produce a purity quotient" (n being the refractive index of purewater.) The numerical value of this quotient varies with the temperatureof the sample. Tl' erefore the temperature of the sample is maintainedconstant within a certain range and an additional temperature correctionis effected. In a preferred form of apparatus for performing themeasuring method, the resultant of the calculation of the quotient isreproduced in both analog and digital form respectively for controllingautomatic process control computers and for actuating a device forindicating the measurements in visible form.

METHOD AND APPARATUS FOR MEASURING THE PURITY RATIO OF INTERMEDIATEPRODUCTS IN SUGAR MANUFACTURE The present invention relates to a methodand apparatus for the automatic continuous measurement of the purityratio of intermediate products in sugar manufacturing.

In the manufacture of sugar, crude juice is first obtained from the rawmaterial. In the case of sugar beets this is done by extraction fromwashed and chipped beets with hot water. In the case of sugarcane, thejuice is squeezed out by roll crushers.

The crude juice thus obtained is purified-for example, by means of thelime-carbon dioxide method-to remove a major portion of the nonsugarsubstances. The resulting thin juice is evaporated in an evaporatorstation to a thick juice, which contains about 60 to 65 percent drysubstance.

The thick juice flows into the sugarhouse where it is boiled tomassecuite, which is a thick mixture of light crystals and dark syrup.The massecuite is cooled in mash troughs and when centrifuged. Themother syrup which is separated by this step is called runoff.

After this separation, and particularly in the production of whitesugar, a washing medium (for example, water) is sprayed on the sugarlayer in'the centrifuge to remove the syrup particles adhering to thesugar crystals. in this process sugar is also dissolved and the washsyrup resulting from a repeated centrifugation has a high sugar content.The centrifuged wash syrup is thereafter further concentrated by boilmg.

The' runoff, or mother syrup from the boiled and centrifuged massecuite,is again boiled, cooled, centrifuged, and washed in a successive stage.

Depending on the type of factory (raw sugar or white sugar factory), thecrystallization and the separation of the sugar are effected in at leasttwo or three successive stages. Runoffs and wash syrups are recycledthrough the various boiling and centrifuging stages in various waysuntil molasses, which is a runoff that can no longer be crystallized, isobtained.

For an economical manufacture of sugar it is important to keep the powerconsumption in the various boiling stages at a minimum and to controlthe process so that molasses with a low sucrose content is obtained. Tothis end it is necessary to measure the various intermediate products(runoffs, wash syrups, and charges of the various boiling stages),giving particular attention to the proportion of pure sucrose in thetotal of nonhydrous substances. This proportion in percentages isindicated by the so-called purity quotient, which is frequently calledthe quotient for short.

The purity quotient is usually written in the form (Pol/Brix)-l00, wherePol denotes the sucrose concentration in degrees S, determinedpolarimetrically according to the lCUMSA method (lntemational Commissionfor Uniform Methods of Sugar Analysis). Brix denotes therefractometrically determined total dry substance content in degreesBrix according to the international sugar scale in the version of 1936,which is still used today.

Since the knowledge of the purity quotient is of paramount importancefor the processing of the intermediate products, the determinations ofthe quotient represent a major part of the work done in the laboratoryof a sugar factory.

' The expenditure in time and energy for the determination of thequotient is relatively great, because the material to be measuredrequires certain preparations. Since the quantities degrees S anddegrees Brix are not equidimensional, the temperature for themeasurement is fixed, according to definition, at C. For measuring thequantity degrees Brix, the sample material is diluted in the proportion1:1 before measurement, then measured at 20 C., and the result is thenmultiplied by the factor 2. For measuring the quantity degrees S, 26grams of the sample material are diluted to make lOO ml. of solution arethen precipitated with lead acetate, then the solution is filtered andmeasured polarimetrically at 20 C.

Due to the preparatory operations the time required for a quotientdetermination is about 20 minutes. Moreover, this conventional method ofquotient determination cannot be fully automated.

Efficient sugar production requires that the proportion of sucrose inthe total of nonhydrous substances-that is, the purity quotient-invarious intermediate products be measured as rapidly, accurately andautomatically as possible. But, improvement in this regard is notpossible using the conventional method of quotient determination.

[t is, therefore, an important object of this invention to provide animproved method for measuring the purity ratio of the intermediateproducts in the sugar manufacture, and to provide such a method which israpid, accurate and which is adapted to being performed automatically.

According to the invention, the angle of rotation a of a sample liquidis determined polarimetrically and thefrefractive index n of the samesample liquid is determined refractornetrically. From these quantities,and from the known refractive index n of pure water, is then formed thequotient a/(n-n which defines the proportion of sucrose in the total ofnonhydrous substances.

The invention will now be described in detail with reference to theaccompanying drawings in which:

HO. 1 is a graph in which the specific rotations a are plotted againstthe refractive indices n for four samples, each having a differentsucrose content, and

the purity quotient in accordance with the invention.

As can be gathered from the graph FIG. 1 every sample yields a straightline whose slope is characteristic of the purity of the sample. Allthese lines start from the value n, as the specific rotation at is zeroat sucrose concentration zero, while the refractive index n has thevalue n n, being the refractive index of pure water. This means that thepurity can, indeed, be described by the new expression a /(nn,,).

The expression a/(n-n,,) is free of concentration-dependent coefficientsof measure and is, therefore, independent of the concentration of thesample. a, which is the function of the difference between tworefractive indices, namely the indices of the levorotatory and of thedextrorotatory polarized light, thus has a different temperaturedependence than the pure refractive index n for nonpolarized light. Itis, therefore, necessary to relate the determination of the quotienta/n-n.) to a constant temperature. This temperature can, however, beselected at random, in contrast to the conventional quotientdetermination which is only exact at 20 C. in the case of temperaturedeviations from the selected reference value, it is possible to make thecorrection by simple mathematics, or by an automatic correction devicein the measuring apparatus.

Since the sample for the measurement of the quotient a/(nn,,) does notrequire special preparation, and since the values for a and n can bemeasured rapidly and with great accuracy, the quotient can likewise bemeasured rapidly and with great accuracy. The method of this inventionthus contributes to the efficiency of the conventional discontinuoussugar-manufacturing process and in addition provides the basis for anautomated, or partly automated continuous manufacturing method.

The quotient a/(n-m) can be related in a simple manner to the purityquotient Pol/Brixit is only necessary to multiply the quotient a/(n-n,,)by a factor F, which takes into account the polarimetric path length,the measuring temperature, and other quantities. The factor F can bedetermined mathematically, but empirical determination by measuring apure sucrose solution, which has according to definition a purityquotient of 100 is preferable. The information content is however, notincreased by relating the quotient a/(nn,)to the purity quotient(Pol/Brix- 100. The information gain apparently achieved by saidrelating is the possibility to make a direct comparison with the valuesobtained by the conventional method. This is not necessary for factorycontrol.

In a preferred manner of using the method of this invention the quotienta/(nn,,) is obtained by translating the angle of rotation at and therefractive index n into electric quantities and forming the quotientalCnelectrically from these quantities and from a corresponding inputvalue for n Also, the quotient thus determined can be multipliedelectrically by the proportionality factor F.

The quotient a/(nn,,) can be used, before or after multiplication by thefactor F, forthe automatic regulation or control of thesugar-manufacturing process. it is advantageous to produce said quotientin both analog and digital form, the analog form being particularlysuited to being fed directly into a process computer for automaticoperation control. The digital form is particularly suited for actuatingan indicating device for reproducing the quotient in visible form.

It has been found expedient to dilute the sample liquid before themeasurement in order to avoid crystallization, and this can beaccomplished automatically.

The measurement of the angle of rotation a and of the refractive index ncan be effected either simultaneously by parallel flow of the sample tobe measured or successively by connecting the measuring points inseries.

ln the automatic formation of the quotient a/(n-n it is advantageous tomeasure the temperature on the material constantly and to automaticallycorrect for the influence of the temperature on the quantities a, n andn Referring now to FIG. 2, magnetic valves 1, 2, 3, 4, and 5 arearranged respectively in five feedlines for different samples. Thesevalves are actuated selectively according to a preset program which iscontrolled, for example, by a process computer. The various feedlinesfor the samples open into a common conduit 6, having a pump 7 therein,and connected to a mixing device 11. A pure solvent, such as water, isalso supplied to the mixing device 11 through another conduit 8 having apump 9 therein. The pumps 7 and 9 are driven by a common motor 10 sothat the same amount of solvent is always added to a given amount ofsample liquid. The mixing device 11 is driven by the motor 12 and may bedesigned as a circulating pump.

From the device 11 suitable conduits 35, 13 at the same time carry someof the diluted sample liquid into a measuring cell of a polarimeter l4and the rest into the measuring cell of a refractometer 15. Thetemperature of the conduits 35, 13 and of said measuring cells iscontrolled, so that there is no temperature drop between the measuringpoints.

The polarimeter 14 is so constructed that it shows the measured value ofthe angle of rotation 11 in digital form at 16. At the same time itproduces the measured value in its analog form as an electric voltagetapped by a precision potentiometer 17.

The refractometer 15 measures the deviation of the refractive index n ofthe sample liquid from the refractive index 11 of pure water. Itproduces the measured value 11-11 in its analog form as an electricvoltage tapped by a precision potentiometer 18.

The electric voltages produced by the measuring instruments 14, 15 areprocessed in a calculating device 19 which calculates the quotientozICrr-n electrically. The device 19 contains resistances 20, 21connecting one end of the output network (viz resistor 26) in serieswith one end of the potentiometer 17; device 19 also includes aresistance 22 connecting the other end of the output network (vizresistor 29) in series with one end of the potentiometer 18. The tap ofthe potentiometer 17 is connected to resistance 23 while the tap ofpotentiometer 18 is connected to resistance 24. Resistances 23 and 24are both connected to an amplifier 25 the amplification factor of whichmay be one, and the amplifier output is connected to the resistor 29 endof the output network. The midconnection of the output network isgrounded, as are also the remaining ends ofthe potentiometers 17, 18.Values of the quotient a/(nn,, of less than 50 do not occur in practice,so that it is reasonable to suppress them for the recording. By means ofthe resistances 26, 27, 28, 29 this suppression is effected so that theoutput voltage at 30 is zero for the quotient 50 and only quotients ofmore than 50 produce an electrical voltage at the output 30.

By means of the resistances 26, 27 28, 29 it is also possible toapproximate the quotient a/(n-n, by means of a correction factor F tothe value of the quotient (Pol/brix)'l00 conventionally determined. Thefactor F may be adjusted by adjusting the resistances 26 and 29.

lt is another object of the calculating device 19 to compensate for thetemperature coefficient of the quotient. For this purpose a thermistor31 is connected into the conduit leading the sample liquid from thedevice 11 to the measuring instruments 14, 15. This thermistor isconnected in series to the resistances 20, 32 which are arranged withinthe calculating device 19. By means of thermistor 31 and resistances 20,32 a temperature coefficient is produced which corrects automaticallythe influence of the temperature of the sample liquid on the quotienta/(nn,,).

For automatic regulation or control of the sugar-manufacturing processan appropriate process control computer (not shown) would have its inputconnected to the output 30 of the calculating unit 19.

In the embodiment illustrated, an analog-digital converter 33 isconnected between the calculating unit 19 and an indicating device 34which shows in digital form the quotient calculated in the unit 19.Alternatively, the analog digital converter 33 could be omitted and theindicating device 34 could be replaced by an indicating device adaptedto show the quotient in analog form.

What is claimed is:

1. A method for measuring the proportion of sucrose in the total ofdissolved substances of intermediate products in sugar manufacturecomprising measuring refractometrically the refractive index n of asample solution of an intermediate product which is to be measured,measuring polarimetrically the angle of rotation on of said sample, andcombining these measurements and the known refractive index n, of purewater in the quotient a/( nn,).

2. The method of claim 1 in which the difference between the refractiveindices n and n is directly measured refractometrically and in whichthis difference and the polarimetrically measured angle of rotation 01are in the form of electric quantities, and in which the respectiveelectric quantities are combined electrically to produce an electricsignal representing the quotient al(nn,,).

3. The method of claim 2 in which the electric signal representing saidquotient is produced in analog and in digital form, whereby said analogform is available for the application to control the operation of aprocess control computer and said digital form is available foroperating an indicating device for reproducing said quotient in visibleform.

4. The method of claim 1 in which said sample is diluted beforemeasurement.

5. The method of claim 1 in which said quotient al( 11-11,) is producedin the form of an electric quantity and in which said quotient iselectrically multiplied by a factor F in order to relate said quotientto the conventional purity quotient (Pol/Brix)'l00.

6. The method of claim 1 in which the difference between the refractiveindices n and n, is directly measured refractometrically and in whichthis difference and the polarimetrically measured angle of rotation 01of the sample solution are reproduced in the form of electricquantities, and in which the respective electric quantities electricallyproduce an electric signal representing the quotient a/(rn furthercomprising measuring the temperature of the sample solution, reproducingelectrically a temperature factor, and multiplying said quotient by saidfactor electrically in order to correct the influence of the temperatureof the sample solution on said quotient.

7. The method of claim 2, in which the electrical signal representingsaid quotient is produced in analog form.

8. The method of claim 2, in which the electrical signal representingsaid quotient is produced in digital form.

9. The method of claim 1, in which the difference between the refractiveindices n and n is measured refractometrically, and in which saidcombining step combines said last-mentioned measurement and saidpolametric measurement.

10. The method of claim 9, in which a temperature measurement is made onthe sample solution, and in which said combining step combines saidtemperature measurement with said quotient to correct the influence ofthe temperature of the sample solution on said quotient.

11. The method of claim 1, in which said measurements are madeconcurrently.

12. The method of claim I, in which the sample solution is continuouslyflowing and in which said measurements are continuously made on separatelike divisions of the sample flow, the first-mentioned measurement beinga refractometric measurement of the difference between the refractiveindices n and n in one of said flow divisions, the second-mentionedmeasurement being made in another of said flow divisions.

13. The method of claim 1, in which said measurements are made at thesame temperature.

14. Apparatus for measuring the proportion of sucrose in the total ofdissolved substances in liquid intermediate products in sugarmanufacture, comprising a mixing device, first conduit means connectedto said device for supplying to said device a sample flow of one suchintermediate product having an unknown sucrose content, second conduitmeans connected to said device for supplying a flow of pure water tosaid device, refractometric means including a measuring cell connectedto the output of said device and accommodating mixed liquid dischargethereby, polarimetric means including a measuring cell connected to theoutput of said device and accommodating mixed liquid discharged thereby,said refractometric means producing an electrical signal outputproportional to the difference between the refractive index n of thesample liquid and the refractive index n, of pure water, saidpolarimetric means producing an electrical signal output proportional tothe angle of rotation 41 of the sample liquid, and quotient-calculatingmeans electrically responsive to said signal outputs and producing anoutput indicative of the quotient a/(nn,,).

15. Apparatus according to claim 14, in which said cells have separateand like connections to the output of said mixing device, whereby theyare simultaneously subjected to like but divided flows of diluted sampleliquid.

16. Apparatus according to claim 15, in which heat-responsive meansproducing an electrical signal output is positioned at the output ofsaid mixing device, said heat-responsive electrical signal output beingconnected in temperature-correcting relation to saidquotient-calculating means.

17. Apparatus according to claim 14, in which said conduits each includea pump, said pumps having a common drive.

2. The method of claim 1 in which the difference between the refractive indices n and no is directly measured refractometrically and in which this difference and the polarimetrically measured angle of rotation Alpha are in the form of electric quantities, and in which the respective electric quantities are combined electrically to produce an electric signal representing the quotient Alpha /(n-no).
 3. The method of claim 2 in which the electric signal representing said quotient is produced in analog and in digital form, whereby said analog form is available for the application to control the operation of a process control computer and said digital form is available for operating an indicating device for reproducing said quotient in visible form.
 4. The method of claim 1 in which said sample is diluted before measurement.
 5. The method of claim 1 in which said quotient Alpha /(n-no) is produced in the form of an electric quantity and in which said quotient is electrically multiplied by a factor F in order to relate said quotient to the conventional purity quotient (Pol/Brix).100.
 6. The method of claim 1 in which the difference between the refractive indices n and no is directly measured refractometrically and in which this difference and the polarimetrically measured angle of rotation Alpha of the sample solution are reproduced in the form of electric quantities, and in which the respective electric quantities electrically produce an electric signal representing the quotient Alpha /(n-no), further comprising measuring the temperature of the sample solution, reproducing electrically a temperature factor, and multiplying said quotient by said factor electrically in order to correct the influence of the temperature of the sample solution on said quotient.
 7. The method of claim 2, in which the electrical signal representing said quotient is produced in analog form.
 8. The method of claim 2, in which the electrical signal representing said quotient is produced in digital form.
 9. The method of claim 1, in which the difference between the refractive indices n and no is measured refractometrically, and in which said combining step combines said last-mentioned measurement and said polametric measurement.
 10. The method of claim 9, in which a temperature measurement is made on the sample solution, and in which said combining step combines said temperature measurement with said quotient to correct the influence of the temperature of the sample solution on said quotient.
 11. The method of claim 1, in which said measurements are made concurrently.
 12. The method of claim 1, in which the sample solution is continuously flowing and in which said measurements are continuously made on separate like divisions of the sample flow, the first-mentioned measurement being a refractometric measurement of the difference between the refractive indices n and no in one of said flow divisions, the second-mentioned measurement being made in another of said flow divisions.
 13. The method of claim 1, in which said measurements are Made at the same temperature.
 14. Apparatus for measuring the proportion of sucrose in the total of dissolved substances in liquid intermediate products in sugar manufacture, comprising a mixing device, first conduit means connected to said device for supplying to said device a sample flow of one such intermediate product having an unknown sucrose content, second conduit means connected to said device for supplying a flow of pure water to said device, refractometric means including a measuring cell connected to the output of said device and accommodating mixed liquid discharge thereby, polarimetric means including a measuring cell connected to the output of said device and accommodating mixed liquid discharged thereby, said refractometric means producing an electrical signal output proportional to the difference between the refractive index n of the sample liquid and the refractive index no of pure water, said polarimetric means producing an electrical signal output proportional to the angle of rotation Alpha of the sample liquid, and quotient-calculating means electrically responsive to said signal outputs and producing an output indicative of the quotient Alpha /(n-no).
 15. Apparatus according to claim 14, in which said cells have separate and like connections to the output of said mixing device, whereby they are simultaneously subjected to like but divided flows of diluted sample liquid.
 16. Apparatus according to claim 15, in which heat-responsive means producing an electrical signal output is positioned at the output of said mixing device, said heat-responsive electrical signal output being connected in temperature-correcting relation to said quotient-calculating means.
 17. Apparatus according to claim 14, in which said conduits each include a pump, said pumps having a common drive. 